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On (he Comparative Evaporative Power of Coal and of Coke. 

 By Andrew Fyfe, M.D., F.R.S.E., F.R.S.S.A. Commu- 

 nicated by the Royal Scottish Society of Arts.* 



In a paper read before the Society hast Session, I stated 

 that the evaporative powder of different kinds of coal, would 

 in practice be found. to be on an average as the proportion of 

 fixed carbon ; for though the gaseous matter evolved from 

 coal by application of heat i&, or ought to be, consumed dur- 

 ing its combustion, yet, as the gases during their evolution 

 from the coal must absorb heat, they will by their consump- 

 tion again supply to a greater or lesser extent that which 

 they absorbed ; hence has arisen the idea entertained by many, 

 that coke will give forth as much heat by its combustion — in 

 other words, will evaporate as much water as will the coal 

 from which it is obtained. Now, though the evaporative 

 power of coal which contains volatile inflammable matter 

 seems to be in proportion to the fixed carbon, it by no means 

 follows that coal, and the coke which it will afibrd, will in 

 practice have the same evaporative power ; and it was with 

 the view of ascertaining whether or not this is the case that 

 the experiments, the results of which I am now to lay before 

 the Society, were undertaken. 



The coal used was that from Tranent, and the coke was 

 that from the same coal, prepared on a large scale in the 

 common way for brewers and others in the neighbourhood. 

 Previous to the trial, they were subjected to analysis to ascer- 

 tain the proportion of volatile matter, fixed carbon, and ashes. 

 The coal was as follows : — 



Coal. 

 Moisture, . . . . . . 13. 



Gaseous matter evolved by heat, . . 34.5 



Fixed Carbon, 60.1 



Ashes, 2.4 



100.0 

 This coal ought therefore to yield 52.5 per cent, of coke, 



• Read before the Royal Scottish Society of Arts, March 28, 1842. 



